1. Field of the Invention
The present invention relates to neghold assemblies for use in photographic printers. In particular, the present invention relates to neghold assemblies that automatically clamp and release film negatives in photographic printers.
2. Description of the Prior Art
One critical component of a photographic printer is the neghold assembly, which holds the photographic film negatives at a print gate where high intensity light is passed through the film negative and imaged onto photosensitive print paper.
The neghold assembly must flatten the film and hold the film securely in position during printing. The film must be as flat as possible so that the entire image within the film is in focus on the photosensitive print paper.
Automatic high speed photographic printers have been developed for first-run production printing in which strips of twelve, twenty, twenty-four or thirty-six exposure film are spliced together for processing and printing purposes. More recently, high speed automatic photographic printers have been adapted to also operate in a reprint production mode in which short segments of film (typically one to four exposures each) are attached to an elongated paper tab.
Both first-run and reprint production in a photographic printer require a neghold assembly which will automatically clamp the film when a desired negative is at the print station or print gate. In both types of printing, the film has a tendency to curl, and the neghold assembly must be capable of flattening the film when it is at the print gate. This is particularly important with reprint production, since the short film strips are typically older and are held only along one edge. As a result, it is more difficult to flatten the film strips in a reprint production operation than in first-run production printing.
One typical type of prior art neghold assembly uses a lower plate or base and a top clamping plate which is pivotally connected to the base. A bias spring biases the clamping plate downward into a normally closed clamping position. A solenoid mounted on the printer has a plunger which extends upward through the base. When energized, the solenoid drives the plunger upward to pivot the top clamping plate to an open position. While this type of neghold assembly has been generally acceptable for first-run production, difficulties have been encountered when attempting to use it for reprint production printing. In particular, with the prior art neghold assembly, flattening and clamping of the short segments of tabbed film has proved to be difficult, since all of the clamping force is provided by the bias spring.
U.S. Pat. No. 3,073,214 by Haviland shows another type of a solenoid operated neghold assembly. The solenoid when energized draws in a plunger which is attached to a lever that pivots on a hanger. One arm of the lever moves downwardly while the other arm of the lever moves upwardly pushing a link upwardly and moving the frame through a linking member to a clamping position as shown in FIGS. 4 and 5 of the Haviland patent. When the solenoid is deenergized, a spring shown in FIG. 7 of the Haviland patent lifts the plunger from the solenoid and moves the frame into a nonclamping position. The neghold assembly of the Haviland patents, however, is not suitable for today's modern high-speed, efficient photographic printers. The linkage from the solenoid to the frame is extremely complicated and the use of knee lever to release the frame from a clamping position for each individual negative of a film strip is inefficient. In an automatic system, the clamping and releasing of the film negative must be done quickly and automatically, and the complicated linkage in the Haviland patent is not conducive to such quick movements. Further, this type of neghold assembly does not afford a quick changeover from one film size to another since the linkage has to be disconnected from the frame and a different frame corresponding to another film size reconnected to the linkage.
Another neghold assembly is shown in U.S. Pat. No. 4,161,365 by Anderson and Wedel. This neghold assembly has quickly changeable bottom and top clamping plates. However, the particular neghold assembly shown is manually operated.
There is a need for an improved neghold assembly (usable in both first-run and reprint production) that quickly and effectively clamps photographic film negatives during printing and quickly releases the negatives to allow the next frame of the photographic film to advance to the print gate.